Rights group says Rohingya rebels killed as many as 99 Hindu villagers in one day in August last year.

Amnesty International says it has evidence that fighters from a Rohingya armed group killed scores of Hindu members of their community in Myanmar's Rakhine state last year.

In a report published on Tuesday, the global rights group said fighters from the Arakan Rohingya Salvation Army (ARSA) rounded up and killed as many as 99 Hindu civilians on August 25, 2017.

The killings in Maungdaw township occurred on the same day ARSA staged attacks on some 30 security posts in Rakhine, Amnesty said.

Those attacks prompted a brutal military crackdown that forced nearly 700,000 Rohingya into neighbouring Bangladesh.

Rohingya refugees said Myanmar's security forces killed and raped hundreds, and set fire to their homes - a campaign the UN said amounted to ethnic cleansing.

The Rohingya are denied citizenship in Myanmar and have long complained of persecution in Buddhist-majority Myanmar.

While the alleged crimes against Rohingya Muslims has been widely documented, Amnesty's report on Tuesday is the first research into abuses committed by ARSA.

Tirana Hassan, Amnesty's crisis response director, said perpetrators of the killings must be held to account.

"It's hard to ignore the sheer brutality of ARSA's actions, which have left an indelible impression on the survivors we've spoken to," she said in a statement.

"Accountability for these atrocities is every bit as crucial as it is for the crimes against humanity carried out by Myanmar's security forces in northern Rakhine state."

Myanmar's military previously accused the Rohingya rebels of killing Hindu civilians, but the armed group has refuted the claim saying it "categorically denies that of its members or combatants perpetrated murder, sexual violence or forcible recruitment".

Maungdaw killings

Citing testimony from survivors and witnesses, Amnesty said masked ARSA fighters rounded up 69 Hindu men, women and children in the village of Ah Nauk Kha Maung Seik and killed 53 of them.

Victims included 23 children - 14 under the age of eight - along with 10 women and 20 men. Only 16 people, eight women and eight of their children, survived.

The survivors, who were abducted and taken to Bangladesh, told Amnesty they were spared after they promised to convert to Islam.

"I asked what they were doing. One of them replied, 'You and [ethnic] Rakhine are the same, you have a different religion, you can't live here'."

Some of the women initially told journalists in Bangladesh that Rakhine Buddhists were responsible for killing Hindu villagers, but later retracted their stories and blamed the Rohingya fighters instead.

Amnesty attributed the inconsistencies to "the pressures and threats to personal safety they faced while in Bangladesh".

Myanmar's security forces uncovered the 45 bodies from Ah Nauk Kha Maung Seik in four mass graves at the site of the killings in September.

Also on August 25, 46 Hindu men, women, and children in the neighbouring village of Ye Bauk Kyar disappeared and were presumed killed by the Rohingya rebels, though their bodies haven't been found.

The group also said ARSA fighters were involved in the killing of six Hindu people on August 26 last year near Myo Thu Gyi village.

Myanmar's government must allow independent investigators, including a UN fact finding mission, access to Rakhine to uncover the full extent of the human rights abuses committed there, Amnesty added.